1. Field of the Invention
This invention relates generally to the decomposition of chlorine from water and more specifically to the use of transition metals, and their compounds, in association with high surface area per mass, for instant autodecomposition of chlorine species to chloride ion and oxygen gas.
2. Description of the Prior Art
Over the years, many attempts have been made to provide an effective system for the removal of contaminants from aqueous systems to provide safe drinking water for human consumption.
Such contaminants include organic compounds such as trihalomethanes as well as inorganic contaminants such as arsenic, cadmium, lead, copper, mercury, chromium and selenium.
Drinking water may also contain various microorganisms such as bacteria, virus, fungus, and protozoa, as well as finely divided and suspended particles derived from soil, silt and inorganic fibers such as asbestos fibers.
For example, ion exchange systems have been employed which employ ion exchange resins such as cation exchange resins to reduce water hardness by exchanging calcium and magnesium for sodium. Chlorine has been found to reduce the effectiveness of such resin materials
Reverse osmosis has also been employed to remove contaminants by the combined action of osmotic pressure and a selective membrane material. Chlorine frequently is found to have a deleterious effect on such membranes.
Activated carbon has recently achieved much popularity in domestic water purification systems, yet it experiences many drawbacks due to its failure to remove a wide range of contaminants from the water as well as its tendency to quickly become relatively ineffective and/or become contaminated with bacteria. Combinations of the above systems have also been contemplated.
Several prior art processes currently in use are as follows: The first process is the use of reducing agents such as sulfur dioxide, bisulfite, or sulfite. The disadvantages of this process are--the costs associated with the use of these chemical reductants, the addition of other ionic species to the water as a result of such oxidation-reduction reactions, the inconvenience of having to use pumps, storage tanks for the chemicals, and meters of various kinds, and long reaction times relative to the instant invention. The Bureau of Reclamation is presently using this approach to dechlorinate water at the Yuma, Arizona Desalting Plant.
A second process is the use of activated charcoal. The disadvantages of this process are--The expense of replacement as the activated charcoal is used up either by the chlorine, organics in the water supply, or bacteria colonies in the charcoal making the process unsafe for drinking water and risky for desalting membranes, and there is only a partial removal of chlorine.
A third process is the use of cobalt and nickel compounds for the autodecomposition of chlorine from water. There are numerous patents on the removal of chlorine from water using cobalt and nickel compounds:
U.S. Pat. No. 1,153,502 to Kriegsheim entitled "Manufacture of Oxygen";
U.S. Pat. No. 1,197,640 to Kriegsheim entitled "Purification of Water";
U.S. Pat. No. 2,520,181 to Teter et al entitled "Process of Preparing Amines and Nitriles from Ammonia and Olefins";
U.S. Pat. No. 3,965,249 to Kinosz entitled "Anti-Pollution Method";
U.S. Pat. No. 4,073,873 to Caldwell et al entitled "Catalytic Decomposition of Hypochlorite";
U.S. Pat. No. 4,297,333 to Crawford et al entitled "Method of Decomposing Hypochlorite ion in a Basic Solution";
U.S. Pat. No. 4,732,688 to Bryan et al entitled "Effluent Treatment";
U.S. Pat. No. 4,764,286 to Bon et al entitled "Catalytic Decomposition of Sodium Hypochlorite in Highly Alkaline Solutions";
U.S. Pat. No. 4,879,047 to Jackson entitled "Effluent Treatment".
Basically, Kriegsheim discovered that "hypochlorite in solution in contact with certain metallic oxides split up smoothly and completely into corresponding chlorides and free oxygen". This is where all of the other patents on the autodecomposition of chlorine in water began. However, all of the prior art in this area have the following disadvantages: No effective way of increasing the reaction rate such that the chlorine is removed almost immediately; Undesirable concentrations of metals in the product water, this is obvious from the chemicals used-undesirable concentrations for drinking water and desalting membranes can be 1 mg/L or less; No data to demonstrate the removal of trace chlorine (a mg/L or less) from water. Regulatory agencies have set below mg/L concentrations of these heavy metals in drinking water. Some publications on the harmful effects of these metals on membranes are:
Murphy, A. P., "Accelerated Deacetylation of Cellulose Acetate by Metal Salts with Aqueous Chlorine", Journal of the Water Pollution Control Federation, Vol. 63, pp. 177-180, 1991.
Murphy, A. P., "Deterioration of Cellulose Acetate by Transition metal Salts in Aqueous Chlorine", Desalination, Vol. 85, pp. 45-52, 1991.
Additional prior art devices are disclosed in U.S. Pat. No. 4,073,873 to Caldwell discloses a process for decomposing large quantities of dilute hypochlorites in aqueous streams wherein hypochlorite ions in aqueous solution are catalytically decomposed by the action of a single-spinel of Co.sub.3 O.sub.4 coated on an inert, stable support.
U.S. Pat. No. 5,039,429 to Laundon et al discloses a process for the removal of hypochlorite groups from aqueous solutions, so as to permit the disposal of the effluent by deep well injection. The invention relates to the catalytic decomposition of such hypochlorite groups from scrubbing water effluent used to remove chlorine from a gaseous effluent, wherein a solid catalyst is dissolved, recycled, and reprecipated in situ. The catalyst is a transition metal, in the group from copper to zinc, and selected from the group consisting of copper, nickel, iron and manganese.
U.S. Pat. No. 5,149,437 to Wilkinson et al discloses a process for removing contaminants from water comprising a filter housing having an inlet at one end for water to be purified and an outlet for purified water at an opposing end, the filter device includes in sequence, first, second and third layers of purification material, a first layer comprising metallic particles which establish a suitable redox potential in the first layer, a second layer comprising activated carbon, and a third layer comprising a weak acid ion exchange resin. The three purification materials must be present in the filter device in the stated order.
None of the patents discuss the use of Raney metals or alumina doped with a transition metal.